or an aliphatic acid of high molecular weight, in short, any acid
which either does not appear in the table or is marked as only •;
soluble in hot water, a few drops of cone, hydrochloric acid will ;
usually precipitate it, and it may then be filtered, or removed •
with ether, and its melting-point determined. If no precipitate is
formed, but the solution turns brown on the addition of an alkali, ;
tannic or gallic acid may be present. If the acid is volatile
and has a distinctive smell (formic, acetic, butyric, etc.), the
solution should] be acidified with sulphuric acid and distilled.
The distillate will contain the free acid, which will probably
have a distinctive smell. Individual tests may then be directly
applied, but it is preferable to neutralise the distillate with
caustic soda and evaporate to dryness on the water-bath, so
as to obtain the sodium salt before testing. The free acid may
be soluble and non-volatile, like oxalic, tartaric, succinic, citric,
etc., and then special tests must be applied (see tests for these :
Phenols.—If it is a free phenol, ether will extract it from its (
aqueous solution. If it is present in alkaline solution, the solution
should first be saturated with carbon dioxide. (N.B.—The alkaline
solutions of catechol, quinol and pyrogallol darken rapidly in
the air.) The following tests should then be applied.
Ferric chloride reaction.—Dissolve a drop of the free phenol 1 *
in water and acid a drop of neutral ferric chloride. A green 1 '
(catechol), blue (orcinol, pyrogallol) or purple (phenol, Jj •
resorcinol) colouration is produced, which is often destroyed by
acid or alkali. Quinol is oxidised to quinone, and turns brown
(p. 193). The naphthols give precipitates of dinaphthol (p. 220). >
Schotlen-Baumann reaction (p. 209).—This may be applied to
the pure phenol in order to obtain thebenzoyl derivative, and the
melting-point determined, or the acetyl derivative may be pre- ^
pared by boiling for a minute with acetic anhydride with the ^
The action of bromine water (p. 180), Liebermann's nitroso-
reaction (p. 180) and the phenolphthalein reaction (p. 186), using
cone, sulphuric acid or zinc chloride, may also be applied.
Alcohols.—It may be a liquid alcohol (methyl, ethyl,
propyl, etc., glycerol, benzyl) or a solution of it in water. In the
former case its boiling-point will have already been determined.
Ittnay be further identified (i) by converting it into the benzole